In general, an existing positioning system is a system using a radio frequency (RF) communication apparatus. As the system using an RF communication apparatus, there are systems based on satellite, ground beacon, wireless LAN (Wi-Fi, WLAN), RFID, active RFID, mobile communication, Bluetooth, UWB, ZigBee, WiBro/WiMax, and broadcasting signals. In order to estimate a position of a user using such a system, several methods have been proposed.
First, there is a recognition-type navigation algorithm used by an RFID-based system. This algorithm is a method used for a system including multiple sensors. In the method, when a user receives a signal from a sensor near the user, only rough position information indicating that the user is positioned near the sensor is provided. Therefore, position accuracy is very low, and continuous positioning is impossible. In addition, a number of sensors such as RFID tags have to be installed, resulting in an increase in cost.
There is a method of calculating a position by estimating intensity of a received signal. It is a method of creating a database of signal intensities at actual and corresponding positions and comparing the intensity of the received signal to the data in the database, thereby estimating a position of a user. In this method, signal intensities at every location are needed by the database. Thus, it takes much time and cost to construct the database. In addition, there is a problem in that the database has to be reconstructed when an indoor arrangement or environment is changed.
Furthermore, there is a method of calculating a position of a user using triangulation by estimating a distance between a transmitter and a receiver from a received signal. This method is currently used the most, and is relatively reliable as compared with the two above-mentioned methods. However, at least three transmitters need to be installed for the triangulation, and this results in a cost increase.
Besides, there is a method of determining a position by estimating an angle between a transmitter and a receiver from a received signal. This method also needs at least three transmitters installed, resulting in a cost increase.
In addition, in a method of determining a position using a distance and an angle between a transmitter and a receiver, the position can be determined only when the transmitters are widely arranged. In addition, in order to determine a distance and a direction, a ranging signal has to be carried on a carrier signal, and the ranging signal is mainly used to determine a position. The ranging signal is easy to use, however, navigation accuracy thereof is low. In contrast, the carrier signal has high navigation accuracy. However, in order to use the carrier signal, ambiguity of the carrier signal has to be solved. So, there is a difficulty in using the carrier signal.
Due to the limitations of the existing methods, there is a need to propose a positioning system for accurately estimating a position of a user at low costs.